In communication networks, particularly wireless communication networks including Evolved Universal Terrestrial Radio Access Networks (E-UTRANs), signal power (also referred to as the signal level), which is proportional to the square of a field amplitude, can significantly and rapidly vary with time. Various mechanisms and models for describing such signal power variations are known, including slow and fast fading, Rayleigh fading, and Rician fading.
Many mobile communication networks, including Long Term Evolution, or LTE, networks based on E-UTRAN, have a cellular configuration. In a cellular network, a mobile terminal communicating via a base station of a first cell may need to search for a second cell, for example in a handover context. In an exemplary scenario, the mobile terminal departs from the first cell and approaches the second cell. Based on signal power detected by the mobile terminal, a base station controller can prepare and decide for a handover of the mobile terminal from the first cell to the second cell. In E-UTRAN and other cellular networks, the first cell, i.e., a Base Transceiver Station (BTS) of the first cell, is not transmitting to and/or expecting transmissions from the mobile terminal during a measurement gap, which allows the mobile terminal to search for the second cell.
Conventional receiver stages comprise an Automatic Gain Control (AGC). The AGC rapidly updates a gain of the receiver stage, which aims at minimizing quantisation noise in the receiver stage. Conventional AGC techniques as described in GB 2 458 542 A measure signal power during portions of a signal and continuously update the gain of the receiver, which is intended to optimize signal reception. EP 1 231 710 A2 describes an automatic gain control circuit operating in a “fast acquire” mode and a “slow track” mode. There also exists an AGC technique according to EP 1 583 232 A2, that stores a gain setting value for a transmission gap.
EP 1 239 606 A1 describes a technique of determining a reference value (RXLEV) during Automatic Gain Control of a general packet control channel, such as the Packet Common Control Channel (PCCCH) of the General Packet Radio Service (GPRS) system designed for the GSM mobile communication system. In a first time interval, one or two measurements are taken from time slots s1 and s2 preceding the PCCCH block to be received. In one embodiment, the RXLEV is calculated based on the measurements in the time slots s1 and s2. The RXLEV for the AGC is updated just before the reception of a new PCCCH block, i.e., a second time interval.
The conventional AGC techniques have been observed to exhibit a loss of measurement time available for cell search within the limited duration of the measurement gaps, which is 6 ms in the case of E-UTRAN. Furthermore, performing a cell search based on a stored gain value setting may fail because of an outdated stored gain value.